Strength and durability studies of multi blended concretes ... · The Indian Concrete Journal March...

The Indian Concrete Journal March 2016 53

POINT OF VIEW

Strength and durability studies of multi blended concretes containing fly ash and silica fume

G.V. Ramana, Malsani Potharaju, N. V. Mahure and Murari Ratnam

It is of significant interest to produce high performance multi blended mix concretes by using supplementary cementatious materials (SCM). In this research an attempt is made to compare the performance of multi blended mix concretes i.e. both binary and ternary mixes with ordinary Portland cement (OPC) concrete. In binary mixes cement was partially replaced by low calcium fly ash (LCFA) or silica fume (SF) and in ternary mixes both LCFA and SF were combined to partially replace OPC. The class F fly ash is used in different proportions of 20%, 30%and 40% and silica fume of 5% and 10% by weight of cement. A constant water binder ratio of 0.42 was maintained. Super plasticizer of required quantity was added to achieve the required degree of workability. The specimens were tested for compression as well as UPV at different ages 7, 28, 56 & 91 days and also the same were subjected to electrical resistance, chloride permeability (ASTM C1202 RCPT test) and under water abrasion (UWA) at both 28 and 91 days. The addition of silica fume with LCFA increased the early age compressive strength as compared to concrete made with fly ash alone; whereas the addition of LCFA up to 30% along with 5% SF exhibited higher compressive strength at later ages and also performed better performances and improved the durability particularly lowered the chloride ion permeability and improved underwater abrasion resistance at all ages than the OPC and other multi blended concrete mixes. The ultra-sonic pulse velocity (UPV) was also carried out on all the multi blended mixes to assess the homogeneity of concrete.

1.0 INtRoductIoNSupplementary Cementitious Materials (SCMs) are widely used in mortars and concretes in various proportions, particularly for reducing the amount of cement which lead to lower both initial and life-cycle costs of concrete structures.

Moreover most SCMs are by-product materials and the use of these materials leads to reduction in waste and savings in energy consumption required to produce cement and blended mix concretes. Most recently the production of multi-blended concretes (MBC) by incorporating industrial by-products/pozzolanic materials is becoming an active area of research due to their improved properties such as workability, long-term strength and durability. According to Jones et al. (1997) [1], the multiple binder combinations are now an option which can be seriously considered for conventional structural concrete. The common blending agents used are fly ash (FA), rice husk ash (RHA), Slag, silica fume (SF), calcined clay and metakaolin. The improved properties such as rheology and cohesiveness, lower heat of hydration, lower permeability, control of alkali silica reaction and higher resistance to chemical attack are reported in the literature (Khan et al., 2000 [2]; and Mehta P. K., 1989 [3]).

In general, each of these materials possesses different properties and reacts differently in the presence of water (Toutanji et al., 2004 [4]) while some have contrasting influences on properties of concrete (Khan et al., 2000). The combination of two or more kinds of mineral admixtures has emerged as a superior choice over single admixture to improve concrete properties (Bagel, 1998 [5]; Pandey et al., 2000 [6]; and Khan et al., 2002 [7]). The research on improvement of the performance of ternary (containing two types of pozzolans) blended cement and binary blended cements (containing one type of pozzolans) nowadays are in progress.

Most of MBC have been based on the use of silica fume with another supplementary cementitious material such as slag or fly ash. It is well known that the addition of silica fume results

The Indian Concrete Journal March 201654

POINT OF VIEW POINT OF VIEW

in considerable improvement of mechanical and durability properties of concretes. Fly ash normally results in lower early strength but improved workability, whereas Silica Fume causes lower workability due to high specific surface but higher reactivity than FA. The effect of combination of SF and FA showed increase in early strength due to the balancing effect in reactivity and water demand. High cost and limited availability of silica fume and construction problems such as dispersion difficulties and increased water demand are some of the drawbacks of using this material in dosages much higher than 5%. Due to relatively low water demand of fly ash, combined use of this material with silica fume can overcome the high water demand of binary mixes containing silica fume. On the other hand increased bleeding and low cohesion which are sometimes attributed to mixes containing fly ash can be overcome through simultaneous use with silica fume.

Recently there has been a growing trend towards the use of supplementary cementitious materials in India and Bhutan for water resources structures. The long-term performance of structural components of hydroelectric power projects such as spillways, stilling basins, overfalls, bridge decks, tunnel lining, energy dissipaters, and dam foundation can be greatly influenced by the durability characteristics. This indirectly affects both initial, life cycle maintenance and repair cost of the structure. The damages to the structural components are caused by various phenomenons such as under water abrasion, alkali silica reaction and chloride ion ingress. In case of hydroelectric constructions, the determination of its durability is very important because of high strategic and economic significance. From the above discussion it can be seen that any attempt to alleviate the deterioration risk therefore implies producing concrete capable of withstanding attack by aggressive agents. The incorporation of low calcium fly ash, silica fume and combinations of both fly ash with silica fume in this research aims at activating this by improving the mechanical properties, chloride ion permeability resistance and under water abrasion resistance of concrete through multi blended mix design.

In this research an attempt is made to develop high performance multi blended normal strength concretes by using SCMs such as low calcium fly ash (LCFA) and silica fume (SF). The performance of multi blended mix concretes i.e. both binary and ternary mixes was compared with ordinary Portland cement (OPC) concrete. Binary mixes were produced by partially replacing by either low calcium fly ash (LCFA) or silica fume (SF) and ternary mixes were produced with the replacement of combination of both LCFA and SF.

The compressive strength, of the above MBC concretes was compared with OPC concrete. The performance of both MBC and OPC concrete was assessed by studying chloride ion permeability and under water abrasion resistance. Further the ultrasonic pulse velocity values were also considered in this study in order to assess the quality of both MBC and OPC concrete.

2.0 INGRedIeNtsThe concrete mix was designed as per of IS: 10262-2004 [8] and it was prepared by using the following ingredients.

2.1.1 Cement43 grade Ordinary Portland cement (OPC) conforming to IS: 8112-1989 [9] was used. The physical and chemical properties of the cement are tested. The equivalent Na2O content is 0.63%.

2.1.2 Coarse aggregateCoarse aggregate from crushed Quartzite rock was used. Flakiness and Elongation Index were maintained well below 15%. Coarse aggregate with a nominal maximum size of 20 mm and a specific gravity of 2.649 was used.

2.1.3 Fine aggregateBadarpur sand (local crushed sand) was used as fine aggregate with a fineness modulus of 2.39 and specific gravity of 2.679. Fine aggregate is classified as zone III as per IS: 2386 (I, III), 1963 [10].

2.1.4 Fly ashLCFA is categorized as a normal pozzolan, a material consisting of silicate glass, modified with aluminium, iron and alkalies. The particles are in the form of solid spheres with sizes ranging from less than 1 µ to 100 µ and an average diameter of 20 µ (Mehta, 1993 [11]). LCFA requires Ca(OH)2 to form strength-developing products (pozzolanic reactivity), and therefore is used in combination with Portland cement, which produces Ca(OH)2 during its hydration. It lowers the heat of hydration and improves the durability when used in concrete as a cement replacement. It also contributes to development of strength due to filler effect inaddition to pozzolanic reactivity. The fly ash used in this research is produced from lignite coal from Badrapur Thermal power plant in New Delhi, India. This fly ash conforms to the requirement of IS: 3812 (Part I) 2003 [12] and also ASTM C-618 [13] type F fly ash (LCFA). It has the total sum of SiO2, Al2O3 and Fe2O3 is >90% but with quite a low CaO content (0.87%).


POINT OF VIEW

2.1.5 Silica fumeSilica fume is a highly reactive material that is used in relatively small amounts to enhance the properties of concrete. It is a by-product of silicon metal and ferrosilicon alloy production. The SF is a very fine powder with spherical particles about 100 times smaller in size than those of Portland cement or fly ash. The particles are extremely fine and having diameter ranging between 0.03 and 0.3μm, with more than 95% of the particles being less than 1μm. Particle size is extremely important for both physical and chemical contributions (ASTM 1240 [14]) of silica fume in concrete. The specific surface of SF is 13 to 20 times higher than other pozzolans. Because of its very high amorphous silicon dioxide content it is very reactive pozzolanic material in concrete. The silica fume reacts with calcium hydroxide to form additional binder material called calcium silica hydrate. Silica Fume (Micro silica) used in this study was obtained from Corniche India Pvt. Ltd., Mumbai, Maharashtra, India. This Silica Fume conforms to the requirement of ASTM C1240.

2.1.6 Superplasticizer (SP) A new generation Poly Carboxylic Ether (PCE) based super-plasticizer, CEMWET SP-3000 (PCE-2) was used. This super -plasticizer is available as a medium brown coloured aqueous solution with standard specifications of ASTM C 494 [15] Type G. The specific gravity and pH value of the super plasticizer is 1.1 and 7, respectively.

2.2 Mix proportions

This paper reports the results of an experimental investigation of short term (early age) compressive strength of multi blended mix concretes. Twelve concrete mix proportions of M30 grade concrete consisting of control, binary and ternary mixes were considered for this investigation as shown in Table 1. The total cementitious material content was kept as 365 kg/m3 and a constant W/B of 0.42 was adopted. In order to get homogeneous samples, the super plasticizer was added to maintain the same slump for all the multi blended concrete mixes.

In CF series, cement (C) was replaced partially with low calcium fly ash (LCFA) by 20%, 30% and 40% for getting CF20, CF30 and CF40 mixes respectively.

In CS series the cement was replaced with silica fume (SF), by (5% and 10%) for getting CS5 and CS10 mixes respectively.

In CFS series cement was partially replaced by both silica fume at (5%, 10%) and fly ash (20%, 30%, 40%) for getting CFS725, CFS635, CFS545 and CFS721, CFS631, CFS541 mixes respectively. For example CFS635 indicates 65% cement, 30%fly ash, 5% silica fume and CFS631 indicates 60% cement, 30%fly ash, 10% silica fume.

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Table 1. Mixes proportions for multi blended concrete mixtures studiedS. no. Mix designation W/B Cement

(Kg/m3)LCFA

(Kg/m3)SF

(Kg/m3)SP

(Kg)CA

(Kg/m3)FA

(Kg/m3)Slump (mm)

1 Control mix (M30) 0.42 365 0 0 1.83 1237 704 50

2 CF20 0.42 292 73 0 2.19 1219 694 50

3 CF30 0.42 255.5 109.5 0 2.56 1210 689 60

4 CF40 0.42 219 146 0 2.74 1202 684 70

5 CS5 0.42 346.75 0 18.25 2.92 1231 701 50

6 CS10 0.42 328.5 0 36.5 3.65 1226 698 50

7 CFS725 0.42 273.75 73 18.25 2.92 1214 691 50

8 CFS635 0.42 237.25 109.5 18.25 3.29 1206 686 50

9 CFS545 0.42 200.75 146 18.25 3.65 1197 681 70

10 CFS721 0.42 255.5 73 36.5 4.8 1208 687 50

11 CFS631 0.42 219 109.5 36.5 4.01 1200 683 50

12 CFS541 0.42 182.5 146 36.5 4.38 1191 678 70



2.3 Casting and testing of specimens

Initially cement, fly ash and SF were mixed to get the total cementitious material. This cementitious material in dry state was mixed with the mixture of fine aggregate and coarse aggregate to produce homogeneous mix. The mixture of water and SP was then added to the dry mix of cementitious and aggregate. Slump cone test was performed as per IS:1199-1959[16] to measure the slump of the concrete. 150 mm x150 mm x150 mm Cube specimens were used to determine both the compressive strength as per IS: 10086-1982[17] and UPV as per IS: 13311 (Part I) 1992[18]. A set of six cubes were

cast as per procedure laid down in IS: 516-1959 [19] for each mix of concrete. After casting, the moulds specimens were air dried for 24 h. The cube specimens were cured for 7 d, 28d, 56d, and 91 days period for conducting compression and UPV tests as shown in Figures 1, 2, and 3. A set of four cylindrical specimens of 50 mm thick and 98 mm diameter were cast for each mix of concrete. These specimens were air dried for 24 hr before they were cured for 28d, and 91 days for performing RCP Test as per ASTM C 1202 [20] and RCPT tests as shown in Figure 4. Further a set of three cylindrical disk specimens of size 100 (dia) mm x 300 (height) mm, were


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cast for each mix of concrete. These specimens were air dried for 24 hr before they were cured for 28d and 91 days for performing UWA test as per ASTM 1138-97 [21] and the average mass loss of the abrasion–erosion is measured at 24-hr, 48hr, and 72 hr and UWA tests as shown in Figures 5 and 6. The underwater abrasion test was carried out up to 72 hr. at intervals of 24hr. The average mass loss (%) observed is the measure of abrasion resistance.

3.0 Results aNd dIscussIoNsThe details of the various tests results were discussed critically to assess the performance of the binary and ternary mixes. These test results cover compressive strength, UPV values, chloride ion permeability and underwater abrasion The compressive strength of test specimens and relative UPV test results of binary mixes (C+LCFA and C+SF) and ternary mixes (C+LCFA+SF) of varies combinations of cementitious materials at 7, 28, 56 and 91 days are shown in Table 2. The

Table 2. Compressive strength and relative UPV of all multi blended mix concretes at each test ageMix ID Compressive strength at different ages (MPa) Relative UPV values (%) at different ages

7 days 28 days 56 days 91 days 7 days 28 days 56 days 91 days

M30 24.6 31.16 33.28 38.38 100 100 100 100

CF20 22.9 30.25 32.18 38.15 104.55 103.44 103.44 103.44

CF30 18.75 28.81 32.82 39.52 110.09 106.88 106.88 106.88

CF40 17.03 25.49 31.24 36.34 103.564 100 100 100

CS5 25.83 33.31 33.62 38.84 106.139 103.442 103.442 103.442

CS10 26.5 34.26 34.38 39.68 111.881 108.031 108.031 108.031

CFS725 24.75 31.64 34.19 39.62 115.248 111.472 111.472 111.472

CFS635 25.15 32.43 34.99 41.5 101.584 101.912 101.912 101.912

CFS545 17.99 26.73 31.12 36.72 109.703 106.119 106.119 106.119

CFS721 19.74 30.05 31.08 36.68 111.089 107.457 107.457 107.457

CFS631 18.99 29.01 32.23 37.12 99.4059 97.5143 97.5143 97.5143

CFS541 16.2 24.92 30.67 35.38 111.881 108.031 108.031 108.031



results of RCPT values of all fly ash binary mix, silica fume binary mixes and ternary mixes at different ages (28d and 91d) were presented in Figure 7.

3.1 OPC + fly ash binary concrete mixes

Figure 8 shows that the variation of the compressive strength with percentage replacement of cement by LCFA at all ages. It was observed that the compressive strength decreased by 6.91%, 23.78% and 30.77% at 20, 30 and 40% replacement levels of LCFA respectively compared to OPC concrete at 7 days. The reduction in compressive strength was less at the age of 28 days with the addition of fly ash up to 40%, the percentage decrease being 2.9%, 7.5% and 11.2% respectively compared to that of OPC concrete. The grater reduction in compressive strength of CF mixes at early ages is considered to be the result of slow development of strength due to delayed setting process. This behavior is an agreement with the findings of the researchers (Mehta (1994) [22], Khan M.I et al (2002) [7]).

The relative strengths of CF20, CF30 and CF40 mixes were 96.69%, 98.62%, & 93.87% at 56 days whereas these strength were 99.40%, 102.97%, & 94.68% at 91 days respectively compared with OPC concrete. It was observed that the binary mix concretes with partial replacement up to 30% LCFA exhibited almost same strength as that of OPC concrete at later ages. The addition of fly ash improved the pozzalanic reaction at later ages due to its higher surface area and glassy phase content. This behavior is an agreement with the findings of the researchers (Mehta (1994) [22], Vagelis G. Papadakis (1999) [23] & M.A. Megat Johari et al (2011) [24]).

Figure 9 shows that the UPV values of concrete increased with the increase of LCFA content up to 30% at both ages (7d, 28 d) for all the mix combinations. The UPV values increased by 4.55%, 10.10% and 2.38% at 20%, 30% and 40% replacement levels of LCFA respectively compared to OPC concrete at 7 days. The increase in velocity at 28 days with 20 & 30% replacement was 3.44% & 6.88% respectively compared with OPC concrete. The addition of fly ash beyond 30% replacement exhibited decrease in velocity.


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In Figure 10 shows the average charge passed (RCPT) decreased by 9.90%, 39.24% and 49.08% at 20, 30 and 40% replacement levels of fly ash respectively compared to OPC concrete at 28 days. The decrease in average charge passed at 91 days with 20, 30 and 40% replacement was 35.29%, 46.90% and 53.43% respectively compared to that of OPC concrete. It was further observed that the chloride ion permeability of fly ash binary mixes reduced with the age of the concrete. However the long term performance of all the CF binary mixes shows low and very low chloride ion permeability. It indicates that with increasing Fly ash content the resistance to chloride permeability of binary mixes is improved. The increased impermeability of the fly ash binary mix may be attributed to the fact of formation of homogeneous mix due to the addition of LCFA to concrete. The addition of LCFA also leads to significant reduction of porosity due to refinement of pore structure of concrete resulting in reduced permeability. This behavior is an agreement with the findings of the researchers (Chindaprasirt et al. [25]). The reduced permeability results in improved long-term durability and resistance to various forms of deterioration.

Figure 11 shows that the mass loss (%) (UWA) increased marginally with the addition of LCFA up to 30%, whereas abnormal increase in mass loss (%) was observed with the addition of fly ash beyond 30% at 28 days. At 91 days, these mixtures with LCFA up to 30% replacement exhibited decreased in mass loss (%). The mass loss (%) increased by 7.34%, 14.58% and 32.61% at 20, 30 and 40% replacement levels of LCFA respectively compared to OPC concrete at 28 days. The mass loss was decreased by 9.96%, 20.54% at 91 days with 20 & 30% replacements respectively whereas it was increased by 12.92% with 40% replacement compared

to that of OPC concrete. The increase in the mass loss (%) of CF mixes at 28 days is considered to be the result of lower activity of the fly ash particles at early ages. The better performance against abrasion at later ages (91days) may be attributed to the fact of improved pozzalanic reaction leading to homogeneous and strong mix. This behavior is an agreement with the findings of the researchers (Tikalsky et al (1988) [26], Naik et al (1995) [27]).

3.2 OPC + silica fume binary concrete mixes

Figure 12 shows that the variation of the compressive strength with percentage replacement of cement by SF at all ages. It was observed that the compressive strength



increased by 5.0% and 7.72% at 5 and 10% replacement levels of SF respectively compared to OPC concrete at 7 days. The improvement in compressive strength was higher at the age of 28 days with the addition of silica fume up to 10%, the percentage increase being 6.9%, 9.95% and 11.2% respectively compared to that of OPC concrete. It is well recognized that addition of SF to concrete provides a significant increase in strength of concrete at early age of hydration. SF also increases the homogeneity and decreases the number of large pores in cement paste, both of which would lead to a higher strength to SF binary mix concretes. This behavior is an agreement with the findings of the researchers (Tahir Kemal Erdem (2008) [28]). The relative strength of the CS5 and CS10 was 101.03% & 103.31% at 56 days whereas the strength was 101.20% & 103.39 % at 91 days compared with OPC concrete. It observed that the binary mix concrete with partial replacement up to 10% SF exhibited higher compressive strength as that of OPC concrete at all ages. This behavior is an agreement with the findings of the researchers (M.A. Megat Johari. et al (2010) [24]).

Figure 13 shows that the variation of the UPV values with percentage replacement of cement by SF at all ages. It was observed that that the variation of the the UPV values of concrete increased with the increase of SF content at both ages (7d and 28 d) for all combinations. The UPV values of concrete increased with the increase of SF content at both ages (7d, 28 d) for all combinations. The UPV velocity increased by 3.56% & 6.14% at 5 and 10% replacement levels

of SF respectively compared to OPC concrete at 7 days. The binary mix consisting of 5%SF did not show any increase in velocity at 28 days where as it showed an increase of 3.44% with the addition of 10% SF replacement. It was further observed that no change in UPV values was noted beyond 28 days indicating that the concrete achieved the maximum homogeneity at the age of 28 days itself. Hence, it can be concluded that the binary mix consisting of SF up to 10% exhibited enhanced quality compared to OPC concrete at all ages.

Figure 14 shows the average charge passed (RCPT) in the OPC and SF blended concrete mixes at the ages of 28 and 91 days. The silica fume binary mixes exhibited the very low chloride ion permeability for both the binary mixes of CS5 and CS10. The average charge passed in the silica fume concrete blends was 80% less than that of the control (OPC) concrete at 91 days and also the charge passed of SF binary mixes are lower than control even at the age of 28 days. The increased impermeability of the SF binary mix may be attributed to the fact that not only to the reduction of permeability of the transition zone around the aggregate in presence of silica fume, but also the reduction of permeability in the bulk paste compared to the hydrated cement paste. In addition, silica fume decreases Ca(OH)2, and further C/S ratio in C–S–H is also reduced. Thus, silica fume concrete is less permeable and highly resistant to aggressive chemical solutions. This behaviour is an agreement with the studies of other researchers Ozyildirim et al (1994) [29] & Sharfuddin Ahmed et.al (2008) [30].


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Figure 15 shows that mass loss (%) (UWA) decreased with the addition of SF up to 10% replacement at 28 days. At 91 days, these mixtures with SF up to 10% replacement exhibited further decreased in mass loss (%). The mass loss (%) decreased by 13.50% & 19.87% at 5 and 10% replacement levels of SF respectively compared to OPC concrete at 28 days. The decrease in mass loss (%) at 91 days with 5 & 10 replacements were 34.56%, 40.22% respectively compared to that of OPC concrete. It has been clearly seen that the inclusion of silica fume in binary blends with Portland cement positively contributes to reduce the mass loss (%) of concrete mix. The densification of the matrix brought about by the pozzolanic reactions of silica fume blocks the pores and results in improving in abrasion resistance of SF blended concrete mixes Toutanji H. et al. (2004)[20]. Hence, it can be concluded that the binary mixes consisting of SF up to10% exhibited better performance to improve the abrasion resistance as compared with that of OPC concrete at both ages.This is in agreement with the findings of Sing Rajbal [31] and Yu-Wen Liu [32].

3.3 Ternary mix concretes (OPC +LCFA +SF)

Figure 16 shows that the variation of the compressive strength of ternary mix concretes consisting of combination of 5%SF with LCFA up to 40% replacement of cement and 10%SF with LCFA upto 40% replacement of cement at all ages. It was observed that the ternary mix concretes consisting of combination of 5%SF and LCFA up to 30% replacement at all ages (7d, 28d, 56d, and 91d) exhibited higher compressive strength than that of ternary mixes consisting of combinations of 10% SF with LCFA up to 30% replacement.

The percentage increases in compressive strength of ternary mix concrete consisting of 5%SF and LCFA up to 30% replacement at 7 days were 0.61% and 2.24% as compared with the OPC concrete. It was observed that the compressive strength of ternary mixes decreased with the addition of SF beyond 5%. The percentage decreases were 19.76% and 23.8% for ternary mixes consisting of 10% SF and LCFA up to 30% replacement at 7days. The percentage increases in compressive strength of ternary mix concrete consisting of 5%SF and LCFA up to 30% replacement at 7 days were 0.61% and 2.24% as compared with the OPC concrete. The addition of SF beyond 5% decreased the compressive strength of ternary mixes. The percentage decreases were 19.76% and 23.8% for ternary mixes consisting of 10% SF and LCFA up to 30% replacement at 7days.

Further it was observed that the compressive strength of ternary mixes increased with the addition of 5% SF beyond the age of 7 days. The percentage increases in compressive strength of ternary mix concrete consisting of 5%SF and LCFA up to 30% replacement were (1.54%, 4.08%), (2.73%, 5.14%) and (3.23%, 8.13%) at 28d, 56d and 91 days respectively as compared with the OPC concrete. It was also observed that the compressive strength of ternary mixes decreased with the addition of SF beyond 5%. The percentage decreases in compressive strength of ternary mix concrete consisting of 10%SF and LCFA up to 30% replacement were (3.56%, 6.9%), (6.61%, 3.16%) and (4.4%, 3.3%) at 28d, 56d and 91 days respectively as compared with the OPC concrete. Hence, it can be concluded that the ternary mix concretes



with 5% SF and LCFA up to 30% replacement exhibited higher compressive strength than that of OPC concrete at all ages.

Figure 17 shows that the ternary mix concretes consisting of combination of 5%SF and LCFA up to 30% replacement at both ages (7d & 28d) exhibited higher UPV values than that of ternary mixes consisting of combinations of 10% SF with FA up to 30% replacement. The percentage increases in UPV values of ternary mixes consisting of 5%SF and LCFA up to 30% replacement at 7 days were 11.88% & 15.25% as compared with the OPC concrete. It was observed that the ternary mixes consisting of SF beyond 5% and LCFA up to 30% showed marginal increase in UPV values. The percentage increases in UPV values of ternary mixes consisting of 5%SF and LCFA up to 30% replacement at 28 days were 8.03% & 11.47% as compared with the OPC concrete. It was observed that the ternary mixes consisting of SF beyond 5% and LCFA up to 30% showed marginal increase in UPV values.

Figure 18 shows that the variation of the charge passed (RCPT) through the ternary mix concretes consisting of combination of 5% and 10%SF with LCFA up to 40% replacement of cement at both 28 and 91 days. It was observed that all the ternary mix combinations exhibited average charge values well below the acceptable limit (Very low). The variation of average charge passed in the specimens with 5% SF are similar to the average charge passed in the specimens with 10% SF except in the ternary blend of 30% LCFA and 5% silica fume (CFS635) which

exhibited lesser decrease in charge passed compared to other ternary mixes. By the use of multi blundered mixes, it is therefore possible to overcome the relatively low 28 day durability performance of LCFA based binary mixes and compared to the control mix, and also substantial increase in chloride ion permeability resistance in later ages has been achieved. Although the binder containing 20% to 40% FA resulted in a decrease in RCPT values, the addition of SF by 5% resulted in a further decrease in RCPT values. However,


POINT OF VIEW

multi blended mix of 30% FA and 5% SF was found to be better than binary blended mixes for resisting chloride ion permeability. The decrease in charge passed with time may be attributed to the change in the pore structure distribution of the hydrated cementitious system due to the use of both fly ash and silica fume in varying proportions. The addition of these SCMS also leads to significant reduction of porosity due to refinement of pore structure of concrete resulting in reduced permeability (Oh et al (2002)[33].

Figures 19 and 20 shows that the variation of the mass loss (%) (UWA) of ternary mix concrete increased with the increase of time period (24hr, 48hr & 72hr) for all the ternary blended mix concretes. The ternary mix concretes consisting of combination of 5%SF and LCFA up to 30% replacement at 28 and 91days exhibited lower mass loss (%) than that of ternary mixes consisting of combinations of 10% SF with LCFA up to 30% replacement. The percentage decreases in mass loss (%) of ternary mixes consisting of 5%SF and LCFA up to 30% replacement at 28 days were 25.38% & 32.07 % whereas the percentage decreases in mass lossas at 91 days were 41.94% & 48.83 % as compared with the OPC concrete. It was also observed that the values of mass loss (%) of ternary mixes increased with the addition of SF beyond 5% at 28days, the percentage increases being 0.22% & 6.37% for ternary mixes consisting of 10% SF and LCFA up to 30% replacement. However the addition of SF beyond 5% with LCFA up to 30%replacemnt exhibited lower mass loss as compared to OPC concrete the percentage decrease being 15.74% & 5.78% at the age of 91 days. Though CFS631 and CFS721 exhibited lesser mass loss, the losses were not

significant compared to CFS635 and CFS725 at the age of 91 days. Hence it can be concluded that the ternary mix concretes consisting of combination of 5%SF and LCFA up to 30% replacement exhibited better abrasion resistance.

4. coNclusIoNsThe following conclusions can be drawn from the above discussions:

The strength of concrete decreased with the increase of LCFA content in all fly ash binary mixes at early ages.

The quality of fly ash binary mix concretes with LCFA content up to 30% replacement at all ages is superior to that of OPC concrete and other fly ash binary mixes.

Among both fly ash and silica fume binary mixes, the silica fume binary mixes produced with the addition of SF up to 10% found to be more resistant against chloride ion permeability and improved underwater abrasion resistance compared with fly ash binary mixes.

The binary mix concrete produced with the partial replacement of cement by LCFA up to 30% exhibited higher compressive strength at later ages. This mix demonstrated higher impermeability, and enhanced homogeneity of concrete.

The binary mix concrete produced with the partial replacement of cement by SF up to 10% exhibited higher compressive strength at all ages. This mix demonstrated higher impermeability, better control of mass loss and enhanced homogeneity of concrete.

The inclusion of SF up to 10% in binary mix concretes contributed to the improved resistance to underwater abrasion by exhibiting low percentage of mass loss. The binary mix concretes produced with addition of LCFA did not show any improvement in the underwater abrasion resistance.

The compressive strength of ternary mixes produced with the addition of LCFA up to 30% along with 5% SF exhibited higher compressive strength at later ages. These mixes demonstrated higher impermeability, improved underwater abrasion resistance and enhanced homogeneity of concrete.

It can be concluded that it is possible to develop ternary mix normal strength concrete better than OPC concrete

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especially with reference to performance in terms of durability. Within the limits of the experimental investigation it is concluded that the ternary mix consisting of combination of 5% SF and LCFA up to 30% demonstrated high performance.

Acknowledgments

The authors gratefully acknowledge and thank the Central Soil and Materials Research Station, New Delhi for giving the opportunity for conducting the experimental work. The authors also gratefully acknowledge and thank GITAM University, Vishakhapatnam. The authors are also acknowledged the thanks to the researchers and writers whose literature was used here for supporting this research paper.

References

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POINT OF VIEW

G.V. Ramana holds a B.Tech and M.Tech. degrees from Andhra University, Visakhapatnam, Andhra Pradesh; pursuing PhD at the Department of Civil Engineering, GITAM University, Visakhapatnam. He is working as Scientist-C at Central Soil and Materials Research Station (CSMRS), Hauz Khas, New Delhi. He has an experience of 10 years in execution of rock mechanics investigations for hydro electric projects and other civil engineering projects. His primary area of interests are rock mechanics and concrete technology.

Dr. M. Potharaju holds a M.tech from JNTU, Hyderabad and PhD from Andhra University. He is a Professor and Registrar in GITAM University, Visakhapatnam. His research interest includes fire resistant concrete, geopolymer concrete, recycled aggregate concrete and ternary mixed concrete.

N.V. Mahure holds a BE from Govt. College of Engineering, Amravati, Nagpur University, Maharashtra. He is a Scientist ‘D’ in Central Soil and Materials Research Station, New Delhi. He has an experience of 24 years in different concretes, diagnostics investigations and health monitoring of concrete structures, review of detailed project reports of hydro-electric projects.

Murari Ratnam holds an MSc. from Delhi University; M.Tech from Indian Institute of Technology, Delhi. He is a Director at Central Soil and Materials Research Station, New Delhi. He has an experience of 36 years in chemistry of construction materials, durability of concrete, water quality, polymer concrete, diagnostic investigation of old structures and promotion of utilization of fly ash in concrete.

Strength and durability studies of multi blended concretes ... · The Indian Concrete Journal March...

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